Phaco thermal control system

ABSTRACT

Control apparatus for an ultrasonic phacoemulsification handpiece utilizes flow rates and temperature measurements as well as power provided to a handpiece for calculating a matrix of power level duty cycle combination that would not generate sufficient heat to create a burn in eye tissue and either prevent operation of handpiece in the matrix or alert a surgeon of such use.

The present application is a division of U.S. Ser. No. 09/599,127, filedJun. 22, 2000 now U.S. Patent No. 6,699,212 which is acontinuation-in-part of U.S. Ser. No. 09/037,638, filed Mar. 10, 1998now U.S. Pat. No. 6,083,193.

The present invention is generally directed to apparatus and a methodfor controlling power delivery to an ultrasonic phacoemulsificationhandpiece as well as controlling fluid flow to and from an eye duringocular surgery with the phacoemulsification handpiece. Moreparticularly, the invention is directed to apparatus and a method forcontrolling phaco power delivery and/or fluid flow based upon the amountof thermal energy delivered to an eye over a specific period of time.

Phacoemulsification of cataracts lenses is a medically recognizedtechnique. The method generally includes making of a corneal incisionand the insertion of a hand held surgical implement, i.e., handpiece,which includes a needle which is ultrasonically driven in order toemulsify the eye lens. Simultaneously, with this emulsified lens and avacuum provided for aspiration of the emulsified lens and insertedfluids.

In order to maintain normal pressure within the eye, a balanced saltsolution is provided as an irrigation fluid and typically supplied froman elevated chamber. Importantly, the irrigation and aspiration of fluidthrough the eye must be carefully monitored in order to maintain normalpressure within the eye during surgical procedures. For example, anunderpressure condition may cause distortion of the eye which often mayinterfere with surgical procedures. On the other hand, overpressure maycause damage to the eye.

As hereinabove noted, pressure in the eye may be controlled by physicalelevation of the source of irrigation fluid interconnected to thephacoemulsification handpiece. Aspiration of fluid is typicallycontrolled through the use of peristaltic pump or the like.

It should be appreciated that the control of irrigation and aspirationfluids is a dynamic problem. For example, during surgical procedures,fragments of broken tissue may temporarily block an aspiration line orthe handpiece. This may lead to a differential pressure which istypically accommodated by stopping or slowing aspiration flow throughthe regulation of the peristaltic pump connected to the aspiration line.

During aspiration of the lens and aspiration fluid, particles mayrestrict the aspiration flow from the eye through an aspiration port inthe tip of the phacoemulsification handpiece. In order to clear thisocclusion, vacuum levels may be increased to create a greaterdifferential pressure across the occluding particle in an effort to movethe particle downstream and away from the eye. Typically, particlesrequire much higher force to start movement than it takes to continuemovement of the particle to the peristaltic pump. Once a particle moves,it creates a subsequent volume of fluid to take up the space it onceoccupied. This volume may be momentarily larger than the volume of fluidin the eye, therefore, producing a momentary-dimpling of the eye.

It has been shown that the pressure sensing of this condition is wellwithin the operation of the phaco machine.

However, of further consideration regarding the utilization ofphacoemulsification handpiece, is the amount of power delivered to thelens by the handpiece in order to fragment the lens. If too much poweris delivered to the handpiece, without concomitant fluid or coolingirrigation fluid, local temperatures of the eye may rise to a levelcausing localized trauma. On the hand, the entire eye may be heatedduring the procedure within the anterior chamber which may cause damage.Thus, it is important to not only control the power delivery of aphacoemulsification handpiece, but to provide a means for calculatingelevated anterior chamber temperatures in order to prevent any tissuedamage due to excess delivered power. Such damage can occur within oneto two seconds under adverse heating conditions.

It should be appreciated that in combination with the occlusion of thephacoemulsification needle, as hereinabove described, the fluid flowingfrom the eye can vary considerably. Thus, heat is not removed from theeye in a generally continuous basis, but, of course, is dependent uponthe actual fluid flow as a function of time. Heretofore, consoles forproviding irrigation fluid and power of an ultrasonicphacoemulsification handpiece and aspirating fluid from the eye duringocular surgery, have not taken into account energy and powerconsiderations nor utilized same for controlling the operation of thephacoemulsification handpiece.

In addition, prior art devices have not provided any warning to surgeonas to impending damage, i.e., burning, to an eye which can be caused byoverheating.

The present apparatus and method provide for such operation.

SUMMARY OF THE INVENTION

Control apparatus, by itself, or for use in a control console forproviding irrigation fluid and controlling power to an ultrasonicphacoemulsification, or cataract extraction, handpiece and aspirationfrom an eye during ocular surgery, generally includes a means formonitoring energy provided to the handpiece and means for monitoringenergy removed from the eye by aspirated fluid. In connection therewith,a computer responsive to input from the means for monitoring powerprovided and removed, provides a means for calculating an energy balanceover a time interval and determining a matrix of power levels and dutycycle combination that will not generate sufficient heat to create aburn of eye tissue. The power may then be regulated in accordance withthe matrix.

In addition, regulation of the fluid flow may also be performed inresponse to the matrix calculation.

More particularly, the means for monitoring power removed from the eyemay include a means for measuring the flow rate of the aspirated fluidand/or irrigation fluid and may further include a means for measuring atemperature difference between the irrigation fluid and the aspiratedfluid.

Additionally, output means, which is responsive to the computer means,may provide an indication of eye temperature based upon the energybalance. Specifically, the output means may provide an alarm at aselected eye temperature level. This enables a continuous monitoring ofthe eye temperature and, in addition, either visual or audible alarm,may be provided at any selected level in order to attract attention toan energy imbalance in order to prevent thermal damage to eye tissue.

Correspondingly, a method for regulating fluid flow and power to anultrasonic phacoemulsification, or cataract extraction, handpiece,includes the steps of monitoring power provided to the handpiece,monitoring power removed from the eye by the aspirated fluid andcalculating, in response to input from the steps of monitoring the powerprovided and the power removed, a matrix of power levels and duty cyclecombinations that will not generate sufficient heat to create a burn ineye tissue. The matrix can then be used to prevent operation of thehandpiece outside the matrix or alert a surgeon of potential burns ifthe handpiece is operated outside the matrix.

Alternately, a test handpiece can be used to determine the matrix andsubsequently used handpiece can be prevented from operation outside thematrix or a warning can be given to a surgeon when a handpiece is usedoutside the matrix.

DETAILED DESCRIPTION

The advantages and features of the present invention will be betterunderstood by the following description, when considered in conjunctionwith the accompanying drawings, in which:

FIG. 1 is a block diagram of control apparatus in accordance with thepresent invention; and

FIG. 2 is a plot of fluid transfer as a function of Phaco powerdisplayed during a phacoemulsification procedure.

Turning now to FIG. 1, there is shown, in functional block diagram form,a phacoemulsification system. The system 10 includes a control console12 for providing irrigation fluid and power to an ultrasonicphacoemulsification handpiece 14, and aspiration fluid from an eye 16during ocular surgery. The console 12 includes a variable speedperistaltic pump 18 which provides a vacuum source, a source of pulsedultrasonic powers 20, and a microprocessor computer 22, an ultrasonicpower level controller 24 and a pump speed controller 26. A vacuumsensor 28 provides input to the computer 22 representing a vacuum levelon an input side of the peristaltic pump 18. Suitable venting isprovided by vent 30. This apparatus and availability is described ingreater detail in U.S. Pat. No. 5,700,240 which is incorporated herewithin its entirety for describing a control console 12 suitable for use inthe present invention.

The console 12 supplies ultrasonic power on line 32 to the handpiece 14and an irrigation of fluid source 34 is coupled to the handpiece 14through line 36. The irrigation fluid and ultrasonic power applied bythe handpiece 14 to a patient's eye, which is indicated diagrammaticallyby block 16. Aspiration of the eye 16 is achieved through line 40.

The power level controller 24 provides a means from monitoring powerprovided to the handpiece 14 by the console 12 and an output indicatinga signal corresponding to the power provided to the handpiece 14 may beseparately imputed to the computer 22 as indicated by the dashed line44.

Any suitable temperature sensors 50, 52 connected to the computer 22 bylines 54, 56 and flow sensors 60, 62 interconnected to the computer bylines 64, 66, respectively, provide a means for monitoring power removedfrom the eye 16 by aspirated fluid. The temperature sensors 50, 52 andflow sensors 60, 62 may be of any suitable type. Since the flow ratesand temperature of the aspiration and irrigation fluids are known, aswell as the power provided to the handpiece, an energy balance can becalculated by the computer.

Energy balance, as the term is used herein, assumes flow through thehandpiece which is not chemically changed, i.e., no chemical reaction ofthe fluid occurs within the eye 16 or the handpiece 14.

The microprocessor computer 22 accordingly is capable of determiningcumulative phaco power delivered over a period of time as well as thecumulative fluid removed from the eye by the peristaltic pump 16. Underthe further assumption of a tight wound and minimal fluid leakage,aspiration flow and irrigation fluid are equivalent in the eye system.Therefore, a correlation is established between the fluid flow, phacopower and heat generation in the handpiece 14. In fact, empirically, theflow rate of irrigation/aspiration fluids may be utilized to determinethe eye temperature given the heat input by the phaco power provided bythe handpiece. In this instance, the fluid temperatures need not becontinually measured or monitored.

As hereinabove noted, decreasing flow coupled with phaco powerdeployment over extended time may result in burns or chamber heating.

The computer 22 utilizes either a look-up table or algorithm todetermine an energy balance and whether the control console 12 shouldcontinue with existing power and fluid settings or switch to modifiedsettings which may be preprogrammed by a user. In addition, the computermay modulate the phaco power level or duty cycle based upon the level ofa “heat factor” determined by the energy balance.

In addition, the computer 22 may provide an output indicated by theblock 70, which may be of an suitable output device or alarm, forproviding an indication of high temperature based on the energy balance.

An example of a heat factor determination with corresponding systemresponse is shown in FIG. 2, which represents an algorithm for handpiece14 operation.

Several methods may be utilized to determine the heat factor inducingmathematical algorithm or a look-up table contained within systemmemory. FIG. 2 illustrates one way in which a heat factor may bedetermined from a two dimensional matrix. FIG. 2 also demonstrates oneexample of how a system may be programmed to respond based upon thedetermined heat factor within this two dimensional matrix.

A combination of change in phaco power as well as duty cycle is shown asa response to ultrasonic power and fluid transfer within a givenincrement of time. By monitoring the fluid removed from the eye by theaspiration means utilizing a microprocessor, the quantity of fluidcapable of transferring heat away from the eye in a given increment oftime can be determined or approximated. In addition, the system 10 isalso capable of monitoring the cumulative ultrasonic energy deployedinto the eye 16 in a given increment of time by utilizing amicroprocessor 22 to either calculate energy directly from the powerlevel utilized by the surgeon via footpedal control, not shown, or bymonitoring equivalent phaco time. Equivalent phaco time is the averagepercent power setting on the system used by the surgeon divided by 100.Heat generation within the eye 16 is a function of the energy deployed.In response to these two calculations, a coordinate is determined withthe two dimensional matrix. The system 10 response to this coordinate iseither provided pre-programmed into the system or determined by thesurgeon and programmed and/or modified in either a preoperative orinter-operative manner.

The equivalent time set for the in FIG. 2 corresponds to full duty cycleof one second. That is, if the handpiece 14 is powered at one-half dutycycle, then the active time would be 2 sec., corresponding to anequivalent time of 1 sec. Full duty cycle.

As hereinbefore noted, the computer 22 may be also programmed tocalculate, or determine, a matrix of power level vs duty cyclecombination that will not generate sufficient heat to create a burn ofeye tissue and either prevent operation of the handpiece 14 in thematrix or alert a surgeon of such use.

A test handpiece (not shown) may be used in the method of the presentinvention to determine the matrix and subsequent handpieces or systemseither prevented from operating outside the matrix or providing awarning to a surgeon when the handpiece or system is operating outsidethe matrix.

Although there has been hereinabove described controlled apparatus inaccordance with the present invention, for the purpose of illustratingthe manner in which the invention is used to advantage, it should beappreciated that the invention is not limited thereto. Accordingly, anyand all modifications, variations or equivalent arrangements which mayoccur to those skilled in the art, should be considered to be within thescope of the present invention as defined in the appended claims.

1. A phacoemulsification system for regulating fluid flow and energyinto an eye during ocular surgery, comprising: a handpiece; a controlconsole configured to provide phaco power to the handpiece, irrigationfluid to an eye; and an aspiration source for removing fluid from theeye; and a matrix comprising phaco power levels and fluid flowconditions that will not generate sufficient heat to create damage toeye tissue within the eye, wherein the system is configured to controlat least one of the phaco power or fluid flow based upon an amount ofthermal energy delivered to the eye over a predetermined period of time.2. The phacoemulsification system of claim 1, wherein the matrixcomprises combinations of phaco power levels, duty cycles, and fluidflow conditions that will not generate sufficient heat to create damageto eye tissue within the eye.
 3. The phacoemulsification system of claim1, further comprising a flow sensor for determining a cumulative amountof fluid removed from the eye over a predetermined amount of time. 4.The phacoemulsification system of claim 1, further comprising at leastone temperature sensor for determining a temperature of at least one ofthe system, the eye, and a fluid within the system or the eye.
 5. Thephacoemulsification system of claim 1, further comprising amicroprocessor for determining the matrix.
 6. The phacoemulsificationsystem of claim 5, wherein the system is configured to adjust a phacopower level based upon the fluid flow conditions.
 7. Thephacoemulsification system of claim 5, wherein the system is configuredto adjust a phaco power duty cycle based upon the fluid flow conditions.8. The phacoemulsification system of claim 5, wherein the system isconfigured to adjust a phaco power level based upon irrigation fluidflow conditions.
 9. A method for regulating fluid flow and energy in acontrol console during ocular surgery, comprising: providing a handpieceand a control console; providing a matrix comprising power levels, powerduty cycles, and fluid flows that will not generate sufficient heat tocreate a bum of eye tissue; and controlling at least one of the phacorower or fluid flow based upon an amount of thermal energy delivered tothe eye over a predetermined period of time.
 10. The method of claim 9,wherein the matrix comprises combinations of the power levels and dutycycles that will not generate sufficient heat to damage eye tissue.